Tools for converting sheets into desired shapes by means of hot forming are known. For instance, the sheets are placed into the tool and acquire their final shape through hot forming. To this end, regions of the tool are typically heated to high temperatures (several hundred degrees). At such temperatures, a considerable amount of heat is transmitted to the environment and thus lost. Means for heating portions of the tool, for instance, heating cartridges, must therefore constantly offset this loss by re-heating, which reduces energy efficiency throughout the sheet forming process. Moreover, parts of tools that operate more optimally at or require a lower temperature are inadvertently heated.
In order to reduce heat transfer between hot parts of tools and the environment or a machine, as well as between parts of tools that have different temperatures, the prior art, such as in US Patent Publication No. 2011/0030442A1, for instance, discloses inserting a gap between tool parts with different temperatures to reduce direct heat transfer between the tool parts during hot forming of the workpiece.